Dr. Charles Vacanti, a Brigham and Women’s Hospital anesthesiologist who is the senior author on one of the papers reporting the discovery and a coauthor on another, said that early this week one of his Japanese coauthors from the RIKEN Center for Developmental Biology notified him of a problem in the paper for which he was a coauthor.

A photo of glowing placental cells was incorrectly included in the paper, Vacanti said. He said that he and his coauthors are submitting a correction to the journal Nature, to remove the extra picture. That problem does not indicate a broader scientific flaw with the work, he said, and added he still expects other laboratories to be able to repeat the technique — an important step in science to show that results are legitimate.

A spokeswoman for RIKEN said in an e-mail that outside researchers alleged improprieties in the data that she would not elaborate on. The institution opened an investigation Feb. 13. Vacanti said there is no such investigation at Brigham and Women’s.

“RIKEN believes that the research results are valid but launched an investigation,” Juliette Savin, a spokeswoman, wrote in an e-mail. “We have asked specialists both outside and inside RIKEN to conduct this investigation.”

Vacanti acknowledged that there has been a “frenzy” around the new papers, but said he remains confident in the findings.

“With regards to the reproducibility of these results, independent groups collaborated on the work reported in the two papers, and STAP cells were independently obtained in those labs,” Rebecca Walton, a spokeswoman for Nature, wrote in an e-mail. “Any paper that is submitted to Nature, independent of its topic, is considered on its own merits and is evaluated carefully according to our editorial procedures.”

The Nature news story reported that Teruhiko Wakayama, a cloning expert who now works at Yamanashi University and is the senior author on one of the papers, said that even he has had trouble reproducing the basic result because there are subtleties to the technique.

Wakayama replicated the technique in his lab before the study was published, but hasn’t done it successfully since then, he told Nature.

“It looks like an easy technique — just add acid — but it’s not that easy,” Wakayama told Nature. “I did it and found it myself. I know the results are absolutely true.”

The RIKEN spokeswoman said that scientists there did not know how long the investigation would take, but that the results would be made public.